Trying to download service p2 getting denied

Could I get help as trying to download Windows XP service pack 2o replace service pack 1 but it gets so far and then I get the message access denied. I done what Microsoft support states to do but I can not find the registry key that I need to enable

However, i think it is saying that it can not verify that you have a valid windows xp install. Correct? If this is the case, just go in internet explorer to the tools menu-> internet options-> advanced tab-> and click the button that says restore to defaults. That should do the trick.